In surgical procedures involving the spine, it is common to secure a pair of spinal rods to a series of vertebrae. Furthermore, it is often necessary or desirable to secure the spinal rods relative to each other.
A spinal rod is often secured to the pedicle portion of a vertebrae by a screw. Surgical procedures involving the spine benefit from minimal invasiveness of the surgery from having a low-profile for any fixtures secured in the body. The ease of recovery and mobility of a patient with spinal fixtures is greatly influenced by the invasiveness of the procedure and by the size of any spinal fixtures.
When utilizing crosslinking or connecting members to secure pedicle screws, a number of obstacles are commonly encountered. Spinal rods are mounted by a surgeon in a custom-fit manner, including some bending of the rod, so that the rod is seated properly along the spine for holding the vertebral portions in proper relation. Accordingly, there is often not a predetermined distance between two spinal rods, and the rods may converge or diverge from each other. In addition, one spinal rod may have a portion directed at an angle different from that of the other rod. Therefore, the central axes of the two spinal rods are skewed or rotated relative to each other.
One attempt at overcoming these obstacles is a transverse connector system which includes two opposed connector ends for securing to spinal rods, with the connector ends secured to each other by a central fastening portion allowing three degrees of movement. That is, the central fastening portion allows the distance between the connector ends to be adjusted by compressing the system, to be pivoted relative to each other around a ball joint, and to be rotated relative to each other.
However, that approach included an internal cavity in one portion of the central fastening portion for receiving a cross rod of the other portion, such that the central fastening portion secures the two portions relative to each other. In such a design, the range of the pivoting movement permitted between the two portions is defined by the size of the internal cavity. In other words, the cross rod can only pivot to a position such that it abuts the wall of the internal cavity. In order to provide a greater sweep, the outer dimension and size of the entire portion must be increased.
Furthermore, it is common for the connecting ends of a connecting member to have a hook portion extending around a spinal rod and pointing back towards the center of the connecting member for securing to a spinal rod. In such an arrangement, installation or implantation of the device requires clearance laterally of the spinal rods so that the hook portion can be placed outside of the spinal rod and then drawn inward for securing on the rod. Often, the patient's soft tissue must be cleared for this purpose, a result which may exacerbate pain, discomfort, and healing time.
In addition, many connecting members utilize set screws. For instance, set screws may be utilized for securing the hook portion to the spinal rod, and a set screw may be utilized for securing one connector end relative to the other. A set screw only provides a line or point contact with the surface against which it is driven. When a set screw drives against a spinal rod or other fixture, damage and distortion may occur at the interface. This can lead to uneven securement by the set screw, localized weakening of the fixture, loosening of the screw, or debris ground from either the screw or the fixture. Additionally, the screws require a threaded path long enough to provide a secure hold for the screw, which adds to the material cost, to the size of the fixture, and to the invasiveness of the procedure. Moreover, use of set screws often requires use of a torque driver to insure the screws are not over-tightened.
Moreover, the use of a set screw in the central fastening area presents a danger to the patient. The connecting member spans the dura portion of the spine. Put simply, portions of the spine other than bone, such as the discs or even the spinal cord itself, may be exposed. Utilization of a set screw in the central fastening area requires using a driver for securing the screw. Using such a driver exposes the non-bone spinal portions to damage caused by the driver slipping from the set screw and punching into the discs or spinal cord in, for instance, in awl-like fashion.
Accordingly, there has been a need for an improved crosslink member for securing spinal rods relative to each other.